Outboard motors which are used to propel watercraft are positioned at the stem of the watercraft, generally attached to the transom. These motors comprise a cowling in which is positioned an internal combustion engine. The engine is arranged to drive a water propulsion device of the motor, such as a propeller.
The motor is connected to the watercraft in a manner which permits the motor to turn from side-to-side about a vertically extending axis for use in steering the watercraft. In addition, the motor is tiltable about a generally horizontal axis for use in trimming the motor.
Because the motor is movably mounted to the craft, it is desirable for the motor to be as small as practical. If the motor extends far beyond the rear of the watercraft, its center of gravity is far offset from the horizontal axis about which it tilts, making it very difficult to tilt the motor. In addition, moving the center of gravity of the motor far from the stem of the watercraft affects the dynamics of the watercraft.
To make the motor small, the cowling in which the engine is positioned is small. This requires the engine to be small to fit within the cowling. The tight confines within the cowling have resulted in past engine designs suffering from several drawbacks.
In general, these engines are arranged so that its crankshaft extends vertically and in driving relation with a vertically extending drive shaft. The drive shaft drives the propulsion device of the motor. The drive shaft can only be positioned so close to the end of the watercraft. That portion of the engine opposite the crankshaft then extends outwardly in the direction opposite the watercraft.
In order to reduce the distance between the rear end of the engine and the crankshaft, the features of the engine may be made smaller. For example, the size of the exhaust pipe extending along the rear end of the engine may be reduced. This, unfortunately, reduces engine performance.
In addition, with the engine so compactly arranged to fit within the cowling, heat build-up often affects the lubricating system. This is especially true when the lubricant path(s) and exhaust passage must be located near one another in the small areas within the cowling which the remainder of the engine does not occupy.
An improved exhaust system arrangement for an outboard motor powered by an internal combustion engine is desired.